Electron tube controlled kelay



March 14, 1950 P. N. MARTIN ELECTRON TUBE CONTROLLED RELAY CIRCUIT Filed Sept. 30, 1948 MQ {Q l Y KENT m w w W Y I N n 5% N m w 5% NRNN NENN y 3% m B 5mm \w w Q m \wmmwr mw W 1 R W 5a m sp flmm Rim a Euw Emw wm m Q. wm ma A- 2 mm R Q w w s E Q -Evw www II Mm Patented Mar. 14, 1950 UNITED STATES PATENT OFFICE County, Pa., ass-ignor to The Union Switch & Signal Company, swissvale Pa a corporation of Pennsylvania Application September 30, 1948, Serial No.51,925

.5 Claims. 1

My invention relates :to electron tube circuits,

andsparticularly to meansfor'chec-king the proper operation of :such circuits when associated with circuits the improper :iailure of which would create :a dangerous condition if not checked.

It has previously been proposed to provide block signaling systems 'for railways in which our indications are secured by the use of fullwave alternating current or half-wave rectified current ofopposite polarities applied to the exit end of the track circuits of the systems at various times .in accordance with traffic conditions. At the entrance end of the track-circuits direct current track relays with associated Lrectifiers are provided and arranged so that one of the relays will be :picked up by half-wave rectified cur-rent of one polarity and the other relay will be picked up by half-wave rectified current of the opposite polarity, and both relays will be picked up by full-wave alternating current.

However, asystemarranged in this manner is subject to unsafe failures ifIa rectifier associated with the track circuit equipment becomes shortcircuited, or -open-circuited,-or -.a combination of both.

'It is well-known in the art that an electron tube and an associated relay may be substituted for a track relay and such a substitution may be readilymade in the system of the type described,

but such an arrangement is subject to similar electron tubecircuits in which failures of a portion of the circuits will not result in an unsafe operation of the equipment associated therewith.

Afurther-object -of my invention .isto provide electron tube circuits which respond only to halfwave rectified current of a predetermined 1pcrlari-ty.

A :further object of my invention is to prowide a railwaysignaling :system employing electron tube circuits-the proper operation of which =is continuously checked.

Other objectsof my invention andfeatures-of novelty therein 'will be apparent from rtheiollowing description taken Lin connection with the accompanying drawing.

In practicing my invention :I provide a first ielectron tube circuit including a. relay .=and an alternating current :source and which is arranged so that when control energy of the proper polarity and phase relationship with respect 'to the alternating current source is supplied to a grid of the tube, the tube will conduct and thus energize the relay. In order to check that the relay associated with the firstelectron tube circcuit is energized only when control energy of a distinctive character vissupplied to the first electron tube circuit, I provide a second electron tube 'circuitiincludingarelay and a source of alternatling current energy which is opposite in phase relationship to thesource provided for the first circuit. The :control energy supplied to the grid of the first tube is also supplied to the grid of the second tube. The tube associated with the second circuit :is arranged to become conductive when the instantaneous polarity of the energy supplied to its anode is positive with respect to the cathode provided the grid of the second tube then has a zero potentialor apositive potential with respect to its cathode. Accordingly, the relay "associated with the .second electron tube :circuit will pickup only when half-wave rectified energy is supplied thereto which is effective to render the first electron tube conductive, but will not pickup on the supply of full-wave alternating current energy to the control grid of the :first :and second electron tube or on the supply of half-wave rectified energy of the :polarity which is not effective :to render the first tube conductive.

I shall describe one form of apparatus embodying myinvention and shall thenvpoint out "the novelieatures thereof in claims.

The accompanying drawing is a diagrammatic view showing the circuits of a three-block,.fourindication railway signaling system employing -e1e ctron tube .icircuits embodying my invention.

It is .to :beunderstood that my invention is not limited to use with electron tube circuits in railway signaling :systems and this one illustration will serve toiiillustrate the manyplaces in-which my invention is useful.

Referring to the drawing, there is shown -.a stretch of railway track over which trafficznob anally 'm'oves Pin the direction indicated :by .an :arrow and which track is formed .by the :usual insulated rail joints '1 into successive sections of a signal system and of which sections #lonly the fullsection ET-and the adjoiningends of the adjacent sections IT-and -3Tare shown'be- .cause'zthese arevsufli'cient for aiull understand- :ing of my invention.

It is to be understood that the equipment, not showmior sections'lT and =3T andthe other 3 Sections is similar to that associated with section 2T.

Each of the sections is provided with a signal for governing movements of trailic into the section, such as signal 25, which governs the movement of traflic entering section ET. The signal may be of any of the well-known types and is here shown as a two unit color light signal, the top unit having a green lamp ZAG, a yellow lamp ZAY, and a red lamp ZAR, and the bottom unit having a green lamp ZBG and red lamp 2BR.

The apparatus associated with each signal includes two relays, ZATR and ZBTR, each having associated therewith a gas filled electron tube VA and VB of the well-known thyratron type and an anode supply transformer ZAT and 2BT, respectively, and a checking relay 2CTR governed by a gas filled electron tube VC of the thyratron type.

A power transformer 2PT is provided for supplying energy to the relays ZATR, ZBTR, and ZCTR, and to the gas tubes associated therewith, a primary winding of transformer ZPT being supplied with alternating current energy from line wires LI and L2 which constitute a power line extending the length of the stretch and which are connected to a suitable source of alternating current energy, not shown.

The lamps of each signal are supplied with energy from a secondary Winding of a lighting transformer 2LT, the primary winding of which is connected to the power line wires LI and L2. The supply of energy to the lamps of the signal is governed by contacts of relay 2ATR and ZBTR to provide different aspects in accordance with traffic conditions in advance of signal 28.

The gas tubes as here shown are of the form in which at least one of the grids is provided with two terminals and between which terminals the grid element is connected in series.

The gas tubes VA, VB, and VC are governed by energy supplied thereto from a coupling impedance or load resistor RI which is connected across the rails at the entrance end of section 2T and is supplied with energy fed over the track rails 5 and 6 from the exit end of the section.

The apparatus at the exit end of the section comprises a track transformer 2TT, a half-wave rectifier KI, and circuits for supplying energy to the rails 5 and 6 which include contacts of relays SATR and 3BTR. The relays 3ATR and SBTR are similar in their operation to the relays 2ATR and ZBTR and are governed by trafiic conditions in section 3T and sections in advance of section 3T.

It is believed that the description of my invention will be facilitated by describing the operation of the system. as a train moves through the various sections.

The apparatus is shown in its normal or clear traffic condition, that is, with no train occupying section ET and at least two sections in advance thereof.

Under normal conditions, half-wave rectified energy of what I shall call negative polarity is supplied to the rails 5 and 6 at the entrance end of the section 2T, and is supplied to the load resistor RI connected across the rails at the entrance end of the section by a circuit which is traced from the left-hand terminal of the secondary winding of transformer ZTT, over rail 6, to the lower terminal of load resistor R! and through the load resistor RI and over rail 5 to the exit end of the section, over basic contact 9 4 of relay 3ATR, over front contact II of relay 3BTR, through the rectifier KI, over front contact I3 of relay 3BTR, and over back contact I5 of relay SATR to the other terminal of the secondary winding of transformer Z'IT,

The instantaneous polarity of the various portions of the circuit and the associated apparatus during one half of the supply energy under normal conditions are designated by plus and minus signs in the drawing, and at the entrance end of the section, it will be seen that the lower terminal of the load resistor RI is positive with respect to the upper terminal during this half cycle. The cathode I I of tube VB is connected to the upper terminal of resistor RI, and additionally connected to the lower terminal of a secondary winding I9 of transformer 2PT, while the upper terminal of secondary winding I9 is connected in series with the shield grid 2| of tube VB and the primary winding 23 of the anode transformer 2BT, and thence to an adjustable tap 25 of resistor RI. It will be seen that at this time the current supplied to the shield grid 2I of the tube VB flows from the lower terminal of the transformer secondary winding I9, to the upper terminal of the load resistor RI, through the load resistor RI to tap 25, through the primary winding 23 of transformer 2BT from the uppermost terminal to the lowermost terminal, and through the shield grid 2| of tube VB to the negative ter minal of secondary winding I9 of transformer 2PT. The anode 27 of tube VB is supplied with energy by a circuit which may be traced from the top terminal of the secondary winding 29 of transformer 2BT through the winding of relay 2BTR, a front contact 3| of relay ZCTR closed in a manner to later appear, and which is connected in multiple with a front contact 33 of relay 2ATR, the anode 21 and the tube space to the cathode I7 of tube VB and to the lower terminal of secondary winding 29 of transformer 2BT. This particular arrangement for supplying the shield grid voltage and the anode energy to the tube VB is fully shown and described in my copending application for Letters Patent of the United States, Serial No. 545,519, filed on July 18, 1944. It is deemed suflicient to point out that the circuit for supplying energy to the shield grid 2| is a series circuit which includes the shield grid 2I, the secondary winding I9 of transformer 2PT, the load resistor RI, and the primary winding 23 of the anode transformer 2BT. Accordingly, an interruption of any portion of the shield grid circuit will cause the supply of energy to the primary winding 23 of transformer ZBT to be cut off, with the result that the energy supplied from the secondary winding 28 of transformer 2BT to the anode circuit of the tube VB including the winding of relay ZBTR will be cut off, so that the tube VB cannot be fired and relay 2BTR cannot be picked up if the voltage applied to the shield grid 2I is lost.

The control grid 35 of tube VB is connected to the resistor RI at the adjustable tap 25 by a circuit which includes in series therewith the limiting resistors R2 and R3 and the control grid 3'! of tube VC, so that the energy supplied to the control grid 35 of tube VB must also be supplied to the control grid 31 of tube VC, since both are in series. The cathode 39 of tube VC as well as the shield grid 4| of tube VC are connected to the upper terminal of resistor RI, as is the oathode I'! of tube VB.

Again the shield grid 41 of tube VA is included in a series circuit that extends from the lower and shield grids of the tube.

terminal of secondary winding M of transformer 2PT through shield grid 41, primary winding 83 of anode transformer 2AT, adjustable terminal 51 to the lower terminal of resistor RI and to the upper terminal of secondary winding 8|.

It follows that during this half cycle of the source of supply the track circuit current flows from the lower to the upper terminal of resistor RI. Consequently, the adjustable terminal 25 is of a positive voltage with respect to the upper terminal of resistor RI. Accordingly, the control grid 35 of tube VB and the control grid 31 of tube VC are both positive with respect to their cathodes. At this time the anode 21 of tube VB is additionally positive with respect to the oathode I1, so that the tube VB is rendered conductive, and the energy which flows through the winding of relay ZBTR causes the relay to pick up its contacts. The anode 43 of tube VC is supplied with energy from the secondary winding 45 of transformer 2PT, which has its upper terminal connected to the anode 43 of tube VC through the winding of relay 2CTR, while the lower terminal is connected to the cathode 39 and the shield grid 4! of tube VC. With instantaneous polarities as shown, the cathode 39 and the shield grid 4| of tube VC are positive with respect to the anode 43, so that the tube is not conductive.

However, during the next half cycle of the alternating current supply voltage under normal conditions, the instantaneous polarities as shown on the drawing are reversed, and current cannot flow through the rectifier Kl at the exit end of the section, so that no energy is supplied to the resistor RI from the track circuit. Also the energy now supplied to the anode 21 of tube VB is negative in potential with respect to the cathode I1 and tube VB is non-conductive regardless of any voltages that may be applied to the control The relay ZBTR is arranged and proportioned to have a slow enough releasing time to bridge the alternate half cycles in which the tube is non-conductive, and the relay remains picked up under clear traflic conditions. With the instantaneous polarities reversed from those shown on the drawing, it will be seen that the polarity of the energy supplied to the anode circuit of tube V is such as to cause the tube to conduct, since at this time there is substantially no control voltage supplied to the control grid 31, and additionally, the shield grid 4I being connected to the cathode has the same potential as the cathode, so that it does not prevent conduction of the tube. Accordingly, the relay 2CTR will be energized during this half cycle, and its front contacts will be pickedup, contact 3I of relayZCTR being closed in the anode circuit of tube VB, to complete the circuit for supplying energy to the winding of relay ZBTR. The relay 2CTR is also arranged and proportioned to be slightly slow in releasing its contacts so that its contacts remain picked up during the alternate half cycles in which the tube VC is nonconductive.

The shield grids of the tubes VA and VB are arranged and connected so that a negative voltage with respect to the cathode is supplied to the shield grid during the time that the anode is positive. As a result, the control grid must have a positive potential at least as great as a given value supplied thereto in-order for the tube to fire at this time. Tube VC has its shield grid connected to its cathode, so that the tube VG S can fire each time its anode is positive, even if no positive control voltage is supplied to the control grid.

From the foregoing, it will be seen that under normal or clear traffic conditions, the apparatus at the entrance end of section 2T is supplied with track circuit current comprising pulses of halfwave rectified energy of negative polarity and the tubes VB and V0 are alternately rendered conductive, and as a result of the relays ZBTR and ZCTR are picked up.

Turning now to the tube VA with its associated relay 2ATR under the normal condition, it will be seen that when the instantaneous polarities are those shown on the drawing, the polarity of the energy supplied from the secondary winding SI of transformer 2AT is such that the anode 53 of tube VA is negative with respect to the cathode 49, so that the tube does not conduct and its associated relay ZATR is deenergized. This shield grid 41 of tube VA is positive with respect to the cathode 49 at this time, but does not influence the action of the tube. Additionally, it will be seen that the cathode .49 of tube VA is connected to the lower terminal of resistor RI, while the control grid 55 of tube VA is connected through a limiting resistor R5 to an adjustable tap 51 of resistor RI. Since at this time the lower terminal of resistor R! is positive with respect to the upper terminal, it will be apparent that the cathode 49 of tube VA is positive with respect to the control grid 55 of the tube, so that the tube is additionally prevented from conducting due to the negative voltage supplied to its grid. During the other half cycle of the supply energy under .normal conditions, the anode 53 of tube VA is positive with respect to cathode 49, but the shield grid 41 is negative in potential with respect to cathode 49 and no control voltage is applied to control grid 55 and the tube VA is retained nonconductive.

From the foregoing, it will be seen that under clear traffic conditions, that is, with section 2T unoccupied and the relays 3A'IR and 3BTR in the positions shown, the relays ZBTR and ZCTR will be energized and their contacts will be picked up, while the contacts of relay '2ATR will be released.

A circuit for supplying energy to the upper green lamp ZAG of signal 28 is established over a back contact 59 of relay ZATR and a front contact 6I of relay ZBTR, while the lower red lamp 2BR of signal 23 is supplied with energy by a circuit including front contact 63 of relay ZBTR. The signal 2S therefore displays an aspect of green over red, denoting proceed.

It will now be assumed that a train moving from left to right passes the signal 2S and enters section 2T. The wheels and axles of the train shunt the energy supplied over the rails 5 and 6 from the exit end of section 2T, so that track circuit current voltage is no longer developed across the load resistor RI at the entrance end of the circuit, and as a result, the supply of positive control voltage to the grid 31 of tube VC and grid 35 of tube VB is out off during the half cycle in which the anode 21 of tube VB is positive. As previously explained, the shield grid 2| is made negative in potential with respect to the cathode I1 by the energy from secondary winding I9 during the half cycle in which the control grid .35 is made positive due to the track circuit current and consequently the tube VB no longer conducts when the section 2T is occupied and the voltage to grid 35 is cut oflf.

7 it is to be observed that tube V is conductive during alternate half cycles of the supply energy the same as before and relay ZCTR is retained picked up while the train occupies the section 2T. Again tube VA is non-conductive when the section 2T is occupied since its shield grid 41 is negative in potential with respect to cathode 49 and substantially no control voltage is applied to control grid 55 during the half cycle in which the anode 53 is positive with respect to the cathode 49. Thus relay ZATR remains released with section 2T occupied.

After a short time interval the contacts of relay 2BTR will release, and when contacts GI and B3 of relay ZBTR release a circuit is established for supplying energy to the upper red lamp ZAR of signal 28 over back contact 59 of relay 2ATR and back contact SI of relay ZBTR, and energy is supplied to the lower red lamp 2BR of signal 28, over back contact 59 of relay ZATR and back contact 63 of ZBTR, so that the signal displays an aspect of red over red, denoting stop.

When the train enters section 3T, relay 3BTR will release in the same manner that relay ZBTR is released when the train entered section 2T. With relay BBTR released its contacts interrupt the supply of half-wave rectified energy of negative polarity to the rails of section 2T and establish the supply of full-wave alternating current energy to the rails of section 2T. If desired, a limiting resistor may be placed in one of the leads to the track rails to limit the current which flows thereto from track transformer 2TT during the time that the track section 2T is occupied by a train.

When the rear of the train vacates section 2T, full-wave alternating current energy is supplied from the exit end of the section over the rails 5 and 6 to the load resistor RI connected across the rails at the entrance end of the section. This circuit may be traced from the terminal of the secondary winding of transformer ZTT designated by the plus sign, over rail 6, to the lower terminal of resistor RI, the resistor RI and over rail 5 to back contact 9 of relay 3ATR, over back contact II of relay 3BTR, and over back contact 65 of relay 3ATR to the other terminal of the secondary winding of transformer ZTT.

As previously described, tube VB will be rendered conductive when the lower terminal of resistor RI is positive with respect to the upper terminal. During the other half cycle of the track circuit current and the upper terminal of resistor Ri is positive with respect to the lower terminal and adjustable terminal 51 is positive with respect to the lower terminal so that control grid 55 of tube VA is positive in potential with respect to cathode 49, the tube VA becomes conductive because anode 53 is now positive in potential with respect to cathode. With tube VA conductive relay ZATR is picked up and it is retained picked up during the half cycles the tube is non-conductive due to its slow release characteristics. With relay ZATR picked up closing front contact 33 an alternative path is closed for the anode circuit of tube VB and that tube is controlled as explained above. Accordingly, at this time the tubes VA and VB will be alternately rendered conductive by the full-wave alternating current energy which is supplied to the resistor RI so that the grids 55 and 35 of tubes VA and VB, respectively, are alternately rendered positive with respect to their cathodes.

From the foregoing, it will be seen that with the train occupying section 3T and section 2T unoccupied; the'full-wave alternating current energy supplied over the rails 5 and 6 of section II to the apparatus located at the entrance end thereof causes the tubes VA and VB to be alternately conductive so that relays ZATR and ZBTR are picked up. -With the contacts of relay 2A'I'R and .relay ZBTR picked, a circuit is established for supplying energy to the upper yellow lamp of signal 28 over front contact 59 of relay 2ATR, while the lower red lamp 2BR of signal 25 is supplied'with energy by a circuit including front contact '63 of relay ZBTR, so that at this time the signal 28 displays an aspect of yellow over red. denoting approach next signal prepared to stop. The relay 2CTR will be deenergized under this traffic condition since by examination of the circuits it will be noted that each time that the anode 43 of tube V0 is positive with respect to its cathode, the energy supplied to the control grid 31 from the adjustable tap 25 of resistor RI will be negative with respect to the cathode 39, so that the tube is prevented from conducting. During the alternate half cycles in which the anode 43 of tube V0 is negative with respect to its cathode, the control grid 31 will have a positive polarity with respect to the cathode but conduction cannot take place at this time since the anode 43 is now negative with respect to the cathode.

When the train vacates section 3T, the relays 3ATR and 3BIR will be picked up, as described in connection with the relays ZATR and ZBTR associated with section 2T. Accordingly, at this time the energy supplied over the rails 5 and 5 of section 2T will be half-wave rectified energy r having a relative positive polarity, that is, energy will be supplied to the track rails during the half cycles in which the polarity is opposite to that indicated on the drawing. During these half cycles energy flows from the right-hand terminal of the secondary winding of transformer Z'IT, over front contact 9 of relay 3ATR, over front contact II of 3BTR, through the half-wave rectifier KI, over front contact I3 of relay 3BTR, over front contact I5 of relay 3ATR, over rail 5 r to the upper terminal of load resistor RI, and

from the lower terminal of resistor RI over the rail 6 to the left-hand terminal of the secondary winding of transformer 2'IT. It will be seen therefore that the energy supplied to resistor RI at this time will consist of pulses of half-wave rectified energy having a polarity such that the upper terminal of resistor RI is positive with respect to the lower terminal.

From an examination of the circuits, it will be noted that during each pulse of the track circuit current the adjustable tap 51 of resistor RI is positive with respect to the lower terminal of the resistor, and the polarity of the energy supplied to the anode 53 of tube VA is positive with respect to its cathode 49. Since the adjustable tap 51 is positive with respect to the lower terminal of resistor RI, it will be seen that energy of positive polarity is supplied through the resistor R5 to the control grid 55 of tube VA, so that the tube is rendered conductive on each pulse of positive half-wave rectified energy supplied over the track rails to resistor RI. As a result, the tube VA will fire on the recurrent half cycles of the energy supplied thereto, and as a result, the contacts of relay 2ATR will be picked up. Also it will be seen that with the upper terminal of resistor RI made positive with respect to the adjustable tap 25 by the track circuit pulses, the cathode I1 of tube VB will be positive with respect to the voltage supplied to its control grid 35 by way of, the control grid 3;! of tube VC and the adjustable tapv 25. Accordingly, each time that the anode 21 of tube VB is positive with respect to its cathode H, the control grid 35 will have a negative polarity with respect to the oathode, so that tube VB is prevented from conducting, and as a result, the relay ZBTR remains released.

Similarly, at this time the energy supplied from adjustable tap 25 of resistor Rl to the control grid 3! of tube V is negative with respect to the cathode 33, so that the tube VC does not conduct and the contacts of relay ZCTR remain released.

With relay 2ATR picked up and the contacts of relay EBTR released, a circuit is established for supplying energy to the upper yellow lamp ZAY of signal 23 over front contact 53 of relay ZATR, and additionally, energy is supplied to the lower green lamp; 238G of signal 2S by a circuit including front contact 53 of relay ZATR and back contact H of relay 2BTR, the contact 63 of relay ZATR interrupting the supply of energy to the lower red lamp 2BR of signal 28. It will be seen therefore, with sections 2T and 3T unoccupied and the section in advance of section 3T occupied, the signal 23 displays an aspect of yellow over green, denoting approach next signal at medium speed.

When the train moving from left to right vacates the section beyond section 3T, relay LlATR will. be picked up, and relay SBTR will be released, and the polarity of the half-wave rectifled energy supplied to the rails of section 21 will be such as to have a relative negative polarity with respect to the rail 6 Under this traffic condition energy is supplied from the left-hand terminal of the secondary winding of transformer ZTT, over rail of section 2T, to the lower terminal of resistor RI, through resistor RI over rail 5 to the front contact Iii of relay SATR, over back. contact I3 of relay 3BTR, through the half-wave rectifier Kl, over front contact 85 of relay 3ATR, over back contact ll of relay BBTR, and over front contact 8 of relay 3ATR to the right-hand terminal of the secondary winding of transformer ZTT. Accordingly, it will be seen that under this trafilc condition the pulses of half-wave rectified energy supplied over the section rails to the load resistor Rt, are of what I have called negative polarity and as a result, the lower terminal of resistor RI is positive with respect to the upper terminal.

The equipment at the entrance end of section 2T now operates in the manner as described originally, that is, under clear trafiic conditions. lhe relay ZBTR will be energized due to. the recurrent conduction of tube VB in response to the pulses of halt-wave rectified energy supplied to its control grid, and relay ZCTR will be energized by the recurrent. conduction of tube VC, sov that relay ZBTR is picked up, and relay ZATR is released, with the result that the signal 2S- now displays its aspect of green over red, denoting proceed.

When the trainvacates the second section be yond section 2T, relay 3ATR will; be released and relay SBTR will be picked up. The equipment has. nowbeen restored to its normal condition previously described.

It will be seen from the foregoing, that the resistor R] is included as a series element in the circuit for supplying energy to the shield grids of tube VA and tube VB. Accordingly, if the resistor Rlv should become open circuited, the supply of energy to. the shield grids. of tube VA and tube. VB would be interrupted, and as a result energy would no longer be supplied through the transformers ZAT and 2BT to the anode circuits of the tubes VA and VB, with the result that relays ZATR and 2BTR would release and remain released. Accordingly, the resistor BI is checked to insure that it does not become open circuited since the resistor would have low enough resistance to take appreciable current from the track and thus provide broken rail protection andgood shunting. sensitivity under high ballast resistance conditions. If one of the section rails 5 or 6 becomes broken, or if the ballast resistance is sufficiently high, and resistor RI becomes open, there will be insufficient current flow in the shield grid circuits for the tubes to supply sufficient energy to the secondary windings of the transformers Z-AT 2B1 to pick up the relays 2ATR and ZBTR. If the rails 5 and 6 are intact and. the ballast resistance between the railsis sufficiently low, then if resistor RI becomesv open, current through the primary windings of transformers EAT and 213T that by-passes Rt through ballast leakage may be of suihcient magnitude to cause the relays ZATR and ZBTR to be picked up when the respective control tubes are rendered conductive, but there is no objection to permitting the relays to operate as usual under these circumstances.

The value of resistance normally required for El is so low that the voltage drops caused by the shield grid currents flowing in portions of RI as described, are negligible compared with the, voltage received from the track rails.

The tube VC and its associated relay ZCTR are provided to check against a possible clear signal failure in the condition where full-wave alternating current energy is. applied to the exit end of section 2T, but relay ZATR fails to pick up due to. an open circuit or other derangement. It will be seen from the foregoing description and exami nation. of the drawing that the anode 43 of tube V0 is positive on the same half cycle as the anode 53 of tube VA, but its control grid will have a negative potential with respect to the cathode 39. if the track section ET is energized on this half cycle. As a result, the tube VC will be rendered conductive and the associated relay ZCTR will be picked up when the, negative half-wave rectified impulses are present in the track section 21, but will not be conductive when the full-wave alternating current energy is present in the section 21 or when the half-wave rectified energy has a pcsitive polarity. Accordingly, if the full-wave alternating current energy is being supplied to the rails 5, and 6, of section 2'1, but the relay ZATR fails to pick up due to a broken wire or other derangement of this circuit, the relay ZCTR will also be deenergized at this time, and as a result the circuitv for relay ZBTR is interrupted, by the front contact 3! of relay ZCTR and front contact 33 of ZATR so that relay 2BTR. remains released. With relays ZATR and ZBTR released, the signal 2S will display an aspect of red over red, denoting stop.

Also, it will be seen that with the circuits for supplying energy to the exit end of section 21? arranged in the manner shown, the failure of rectifier KI can only cause a more restrictive indication to be displayed by the signal 23; than would otherwise be displayed if the rectifier were intact and operating properly. For example, should the traffic conditions in and ahead of. section 3T be such that the apparatus at the exit. end of section 2T is conditioned to supply pulses of half-wave rectified energy having a negative polarity to these section rails, as shown in the drawing, and the rectifier Kl should become short-circuited, it will be seen that fullwave alternating current energy will then. be supplied to the section rails and 6 of section 2T. Accordingly, the relays ZATR and ZBTR will be picked up, and their contacts will establish the circuit previously described for supplying energy to the upper yellow lamp 2AY of signal 28 and the lower red lamp 2BR of signal so that the signal displays an aspect of yellow over red denoting approach next signal prepared to stop. If the rectifier Ki should become open-circuited, no energy will be supplied to the section rails 5 and 6 and the relays 2ATR. and 2BTR will be released, so that the signal 23 displays a red aspect, denoting stop.

Although I have herein shown and described only one form of electron tube circuits embody ing my invention, it is to be understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a first, and a second electron tube circuit, each comprising an electron tube having at least an anode, a cathode and a control electrode and having a winding of a relay in series with its anode, whereby the relay is energized when the tube is rendered conductive by the application of control voltage to the control electrode of the tube, a couplin impedance, said control electrodes being connected to said coupling impedance, so that the voltage drop across said coupling impedance caused by the flow of current therethrough is impressed on said control electrodes and said control electrodes being connected to said coupling impedance so that the polarity of the energy supplied from said coupling impedance to the control electrode of said first tube is opposite in polarity to the energy supplied from said coupling 1m pedance to the control electrode of said second tube, means for at times supplying unidirectional pulses of current of one polarity or the other to said coupling impedance, means for at other times supplying alternating current energy to said coupling impedance, a circuit gOV- erned by contacts of said first and second relays, and means for checking the response of said first and second tubes to alternating current energy supplied to the control electrodes of said tubes, said last named means comprising a third electron tube having a relay in its anode circuit and arranged to become conductive when energy is supplied thereto from said coupling impedance which is effective to cause said sec ond tube to become conductive and arranged to be non-conductive when energy is supplied thereto from said coupling impedance which is effective to cause said first tube to become conductive.

2. In combination, a first, a second and a third electron tube each having an anode, a cathode and a control electrode; a relay for each of said tubes, a source of alternating current, a load circuit including a coupling impedance, supply means including a rectifier and operable to dif-- ferent positions to connect said source to said load circuit to supply rectified current of negative or positive polarity or alternating current to the load circuit according to the position of the supply means, a power transformer receiving energy from said source, an anode circuit for each of said tubes having connections to the anode and cathode of the tube and including a secondary winding of said transformer and a winding of the respective relay, said control electrodes connected to terminals of said coupling impedance so that the voltage applied to the control electrode of said first tube is opposite in phase to the voltage applied to the control electrodes of said second and third tubes, said tubes connected in a manner for said first tube to be conductive to energize its relay in response to rectified current of positive polarity supplied to the load circuit for said second tube to be conductive to energize its relay in response to rectified current of negative polarity supplied to said load circuit and said third tube to be made conductive to energize its relay during the half cycle of the alternating current source when no current is supplied to the load circuit when rectified current of negative polarity is supplied thereto, two alternate paths one including a front contact of the relay of said first tube and one including a front contact of the relay of said third tube interposed in the anode circuit of said second tube, and circuits selectively controlled by said relays of said first and second tubes.

3. In combination, a first and a second electron tube each having an anode, a cathode and at least one control electrode; a source of alternating current, a load circuit including a load resistor, supply means including a rectifier and operable to diiiferent positions to connect said source to the load circuit to supply rectified current of one relative polarity or rectified current of the other relative polarity or full-wave alternating current according to the position of the supply means, a power transformer receiving power from said source, a relay for each of said tubes, an anode-cathode circuit means for each of said tubes having connections to the anode and cathode of the respective tube and including a secondary winding of said transformer and a winding of the respective relay, a control circuit for each of said tubes having connections to the control electrode and cathode of the respective tube and to a selected terminal of said load resistor, said control circuits disposed for said first tube to be conductive to energize its relay when rectified current of said one relative polarity is supplied to the load circuit and for said second tube to be conductive to energize its relay when rectified current of said other relative polarity is supplied to said load circuit and for both tubes to be conductive and both relays energized when alternating current is supplied to said load circuit, a controlled device operable to different positions and selectively controlled through contacts of the relays of said first and second tubes, a checking electron tube and relay, said checking tube having an anode, a cathode and a control electrode and provided with an anode-cathode circuit connected to the anode and cathode of the tube and including a secondary winding of said transformer and a winding of said checking relay, said checking tube also provided with a control circuit connected to its control electrode and to said load resistor and disposed to permit the checking tube to be conductive to energize the checking relay when rectified current of said other relative polarity is supplied to the load circuit, but not when rectified current of said one relative polarity or alternating current is supplied to the load circuit, and a front contact of said checking 13 relay and a front contact of the relay of said first tube interposed in multiple in the anodecathode circuit of said second tube.

4. In combination, a first and a second electron tube each having an anode, a cathode and at least one control electrode; a source of alternating current, a load circuit including a load resistor, supply means including a rectifier and operable to different positions to connect the load circuit to said source to supply rectified current of one relative polarity or rectified current of the other relative polarity or full-wave alternating current according to the position of the supply means, a power transformer receiving power from said source, a relay for each of said tubes, an anode-cathode circuit means for each of said tubes having connections to the anode and cathode of the respective tube and including a secondary winding of said transformer and a winding of the respective relay, a control circuit for the two tubes and having connections to the control electrodes and cathodes of the tubes and to a terminal of said load resistor, said two anodecathode circuit means and said control circuit provided with connections for said first tube to be made conductive and its relay energized in response to rectified current of said one relative polarity supplied to said load circuit due to a given position of the supply means and for said second tube to be made conductive and its relay energized during the half cycle of the alternating current no current is supplied to the load circuit for said given position of the supply means, and a front contact of the relay of said second tube interposed in the anode-cathode circuit means of said first tube.

5. In combination, two electron tubes each having an anode, a cathode and a control elec- 14 trode; a relay for each of said tubes, a source of alternating current, a transformer receiving energy from said source, an anode-cathode circuit means for each of said tubes having connections to the anode and cathode of the tube and including a secondary winding of said transformer and a winding of the respective relay; a load resistor, means operable during a given time to supply to said load resistor from said source rectified current of a given polarity, a control circuit for the two tubes having connections to the cathodes of the tubes in multiple and to the control electrodes of the tubes in series and to said load resistor, said control circuit and said anode-cathode circuit means poled for a first one of said tubes to be conductive and energize its relay in response to said rectified current supplied to said load resistor and for a second one of said tubes to be conductive to energize its relay in response to the half cycle of the alternating current from said transformers that cur rent is not supplied to said resistor during said given time, and a front contact of the relay of said second tube interposed in the anode-cathode ircuit means of said first tube.

PAUL N. MARTIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,629,866 Grondahl et a1 May 25, 1927 2,221,653 Place Nov. 12, 1940 2,412,092 Mayle Dec, 3, 1946 2,428,125 Nicholson Sept, 30, 1947 

